There is nothing wrong with a really good stock carbs setup. This would mean choke plates removed, primer install, tamper caps removed, T-handles installed, accel pump removed, returns drilled, and restrictor used. Switching to novis will give you at most 1 mph more. A good stock carb setup will give you great results. The bigger novis will give you a little more but again they are BIGGER. With that said I run 48 Novis.

Vf-3 reeds give big gains in snap and quickness compared to any reed on the market for the gpr. With saying this I did NOT see much gains with the vf-3 reeds on a GP setup.

Moto tassinari get these results by incorporating more reed petals per reed cage. This allows the same to more air flow with the reed petals opening only half the distance. This allows them to close and open faster.

On the OEM carbs do they have posted proven jetting specs for a 1390 motor? and what type of motor Lowell, TJ or GroupK? I have not seen much on this and am still working with a couple guys on Lowell ported 1390's. The groupK motor jetting is known.